[media] sh_vou: remove current_norm

The current_norm field is deprecated and is replaced by g_std. This driver
already implements g_std, so just remove current_norm.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Acked-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>